A typical alternating-current surface discharge type panel used as a plasma display panel (hereinafter referred to as “panel”) has many discharge cells between a front plate and a back plate that are faced to each other. The front plate has the following elements:
a plurality of display electrode pairs disposed in parallel on a front glass substrate; and
a dielectric layer and a protective layer for covering the display electrode pairs.
Here, each display electrode pair is formed of a pair of scan electrode and sustain electrode. The back plate has the following elements:
a plurality of data electrodes disposed in parallel on a back glass substrate;
a dielectric layer for covering the data electrodes;
a plurality of barrier ribs disposed on the dielectric layer in parallel with the data electrodes; and
phosphor layers disposed on the surface of the dielectric layer and on side surfaces of the barrier ribs.
The front plate and back plate are faced to each other so that the display electrode pairs and the data electrodes three-dimensionally intersect, and are sealed. Discharge gas containing xenon with a partial pressure of 5%, for example, is filled into a discharge space in the sealed product. Discharge cells are disposed in intersecting parts of the display electrode pairs and the data electrodes. In the panel having this structure, ultraviolet rays are emitted by gas discharge in each discharge cell. The ultraviolet rays excite respective phosphors of red (R), green (G), and blue (B) to emit light, and thus provide color display.
A subfield method is generally used as a method of driving the panel. In this method, one field is divided into a plurality of subfields, and light is emitted or light is not emitted in each discharge cell in each subfield, thereby performing gradation display. Each subfield has an initializing period, an address period, and a sustain period.
In the initializing period, an initializing waveform is applied to each scan electrode, and initializing discharge is caused in each discharge cell. Thus, wall charge required for a subsequent address operation is formed on each discharge cell.
In the address period, a scan pulse is sequentially applied to scan electrodes (hereinafter, this operation is referred to as “scan”), and an address pulse corresponding to an image signal to be displayed is applied to data electrodes (hereinafter, this operation is referred to as “address”). Thus, address discharge is selectively caused between the scan electrodes and the data electrodes, thereby selectively producing wall charge.
In a subsequent sustain period, as many sustain pulses as a predetermined number corresponding to the luminance to be displayed are alternately applied to the display electrode pairs formed of the scan electrodes and the sustain electrodes. Thus, discharge is selectively caused in the discharge cell where wall charge has been produced by address discharge, thereby emitting light in this discharge cell. Image display is thus performed.
The plurality of scan electrodes are driven by a scan electrode driving circuit, the sustain electrodes are driven by a sustain electrode driving circuit, and the data electrodes are driven by a data electrode driving circuit.
As one example of the subfield method, the following driving method is disclosed. Initializing discharge is caused using a gently varying voltage waveform, initializing discharge is selectively caused in the discharge cell having undergone sustain discharge, and thus the light emission related no gradation display is minimized to improve the contrast ratio.
Specifically, in the initializing period of one of a plurality of subfields, the all-cell initializing operation of causing initializing discharge in all discharge cells is performed. In the initializing period of other subfields, the selective initializing operation of causing initializing discharge only in the discharge cell that has undergone sustain discharge in the immediately preceding sustain period is performed. As a result, light emission that is not related to the display is only light emission following the discharge of all-cell initializing operation, thereby allowing image display of sharp contrast (for example, patent literature 1).
Thanks to such driving, the luminance (hereinafter referred to as “luminance of black level”) in a black display region that is varied by light emission related to no image display is determined only by weak light emission in the all-cell initializing operation, and image display of sharp contrast is allowed.
A technology of stabilizing the initializing discharge is disclosed. In this technology, in the initializing period, positive voltage is applied to scan electrodes, and then negative voltage is applied to the scan electrodes for a period shorter than the period when the positive voltage is applied. Then, erasing discharge is caused in the discharge cell where positive abnormal wall charge is accumulated on the scan electrode, and abnormal wall charge is erased. Thus, the initializing discharge is stabilized (for example, patent literature 2). When new discharge is caused in order to adjust the wall charge after the initializing discharge, however, problems such as increase in power consumption and degradation of luminance of black level occur.
Recently, the definition of the panel has been further improved. However, in the discharge cell fined in response to improvement in definition of the panel, it is recognized that a phenomenon called “charge decreasing” is apt to occur. In this phenomenon, the wall charge produced in the discharge cell by the initializing discharge is lost.
When excessive wall charge is accumulated in the initializing period, however, strong address discharge occurs in the subsequent address period. It is recognized that the wall charge decreases due to the address discharge occurring in other discharge cells. When strong address discharge occurs in a certain discharge cell, much wall charge is lost and a discharge failure can occur during address operation in the discharge cells adjacent to the certain discharge cell.
While, when the wall charge accumulated in the initializing period is insufficient, a phenomenon (unlit cell) occurs where address discharge itself does not occur and light emission does not occur in a discharge cell to emit light.
Therefore, in order to cause stable address discharge, it is important to appropriately adjust the wall charge in the initializing operation.    Patent Literature 1 Unexamined Japanese Patent Publication No. 2000-242224    Patent Literature 2 Unexamined Japanese Patent Publication No. 2005-326612